Iliocostalis lumborum is the lateral column of the lumbar erector spinae, providing the primary lateral lumbar flexion force and contributing substantially to lumbar extension. It is the largest component of the lumbar paraspinal mass.
| Origin | Posterior iliac crest and sacrum via the thoracolumbar fascia |
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| Insertion | Inferior borders of ribs 5-12 — angles |
| Nerve Supply | Dorsal rami of lumbar spinal nerves (L1-L4) |
| Blood Supply | Segmental lumbar arteries |
| Actions | Extends the lumbar spine; Ipsilateral lateral lumbar flexion — the most powerful lateral flexor in the lumbar region; Assists depression of the lower ribs |
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Iliocostalis lumborum is one of the primary muscles assessed in chronic low back pain — its cross-sectional area on MRI correlates with pain chronicity and disability. In lumbar spine surgery, this muscle along with the longissimus is retracted to access the posterior elements. Minimally invasive approaches preserve the iliocostalis to reduce post-operative atrophy.
The lateral paraspinal muscle mass — palpated at the lumbar level lateral to the spinous processes.
MRI cross-sectional area reduction of iliocostalis lumborum correlating with lumbar pain chronicity and disability, used as an objective outcome measure in rehabilitation trials.
